1. Field of the Invention
This invention relates to a packaging material for photosensitive materials such as photographic photosensitive materials.
2. Description of the Prior Art
As the packaging material for photographic photosensitive materials, it is necessary that various properties be present such as light-shielding, moistureproofness, gas barrier and physical strength, and various packaging materials have accordingly been developed.
Among them, there are the packaging films consisting of a flexible sheet and a thermoplastic resin film containing a light-shielding material laminated on one side of the flexible sheet. The flexible sheet is a metal foil or an aluminum-metallized film such as aluminum-metallized nylon resin film, aluminum-metallized polyester resin film, aluminum-metallized polyethylene resin film, aluminum-metallized polypropylene resin film or the like, and the thermoplastic resin film is high pressure low density polyethylene (LDPE) resin film, linear low density polyethylene (L-LDPE) or the like. These packaging films exhibit a strong tendency to curl, and bag-making is difficult.
In an attempt to counteract the curling tendency another flexible sheet was laminated on the other side of the flexible sheet so as to decrease curling. The another flexible sheet laminated was heat-resistant, and it was paper, nonwoven fabric or various thermoplastic resin films, such as nylon resin film, polyester resin film, high density polyethylene resin film or polypropylene resin film, being biaxially stretched, uniaxially stretched or unstretched and containing or not containing a light-shielding material. In order to decrease curling, the another flexible sheet to be laminated a similar composition and a similar thickness and contained a light-shielding material. Examples of such conventional packaging films are illustrated in FIG. 18 to FIG. 21.
The packaging film of FIG. 18 consists of a light-shielding LDPE resin film layer 10a, an aluminum foil layer 11 laminated thereon through an adhesive layer 5 and a bleached kraft paper flexible sheet layer 1 laminated thereon through an adhesive layer 5.
The packaging film of FIG. 19 consists of the packaging film illustrated in FIG. 18 and another light-shielding LDPE resin film layer 10a laminated on the flexible sheet layer 1 through an adhesive layer 5. This packaging film was employed for packaging the photographic photosensitive material requiring strong physical strength such as a weight roll of a photographic photosensitive material.
The packaging film of FIG. 20 consists of an aluminum foil layer 11 and two uniaxially stretched light-shielding film layers 12a laminated on both sides of the aluminum foil layer each through an adhesive layer 5 (U.S. Pat. No. 4,331,725).
The packaging film of FIG. 21 consists of a metallized thermoplastic resin film layer 16 composed of a thermoplastic resin film layer 14 and a metallic membrane layer 13 and two light-shielding polyethylene polymer layers 15a containing more than 50 wt. % of L-LDPE resin and a light-shielding material laminated on both sides of the metallized thermoplastic resin film layer 16 each through an adhesive layer 5. The strength and the difference in the layer thickness of both polyethylene polymer layers 15a were specified (Japanese Patent KOKAI No. 61-54934).
However, the packaging film of FIG. 18 was insufficient in the removal of curling, and it required special bag-making conditions. It was expensive, and packaging workability was poor. While, in the cases of the packaging materials of FIG. 19, FIG. 20 and FIG. 21, curling was improved, and bag-making was good. However, they were thick and stiff, and packaging workability was poor. They were also expensive. Moreover, when carbon black was blended as the light-shielding material, since the surface layer contained carbon black, their commercial values were low. Furthermore, since the exposed surface layer was almost the same as the reverse surface layer, heat resistance of the exposed surface layer was insufficient. As a result, heat-sealed portions of the surface layer melted not only to make its appearance poor but also decreased the physical strength of the heat-sealed portion. Additionally, the surface tended to be worn away during transportation, and the black powder generated stained the packaged or other products.
As the conventional packaging material for packaging heavy photographic photosensitive materials having sharp edges such as a roll film for movie, the packaging materials shown in FIG. 18 to FIG. 20 and FIG. 32 were employed.
The packaging material of FIG. 32 consists of a foamed sheet 26 and two uniaxially stretched light-shielding film layers 12a laminated on both sides of the foamed sheet each through an adhesive layer 5 (U.S. Pat. No. 4,565,733).
However, as the packaging material for packaging heavy photographic photosensitive materials having sharp edges, the packaging material of FIG. 18 was weak in physical strength. The packaging material of FIG. 19 was punctured by the sharp edge of a photographic photosensitive material. The inside surface layer was abraded to generate black powder, and it adhered on to the photographic photosensitive material. This caused developing troubles. The packaging material of FIG. 20 was remarkably improved in tear strength. However, since this packaging material was poor in buffer action, it was sometimes punctured by the sharp edge. It had also problems in heat-sealing strength and heat sealability. The packaging material of FIG. 32 was excellent in physical strength such as tear strength. However, it had a problem in bag-making, and bag-making ability in an automatic bag-making machine was particularly poor. Moreover, cutting waste of the uniaxially stretched film was generated in quantity, and it became expensive.
Some packaging materials are required tearability by hand. Uniaxially stretched film was usually employed for the packaging materials. The inventor has once prepared a packaging material consisting of a laterally uniaxially stretched high density polyethylene film layer, an aluminum foil layer laminated thereon through an adhesive layer and a light-shielding LDPE resin film layer containing carbon black further laminated thereon through an adhesive layer. The tearability of this packaging material was good. However, it was punctured at its corners during packaging or transportation, and therefore, moistureproofness and light-shielding could not been secured. The tearability of the aforementioned packaging materials such as shown in FIG. 19 was bad, and scissors were necessary for opening the package. In the case where scissors could not be used, the removal portion for photosensitive materials was partially sealed by dotted line seal, and in order to secure light-shielding and moistureproofness, the removal portion was turned and fixed by an adhesive tape. In the case of assembly packaging, since the folded portion contacted the packaged photosensitive materials, indentations or fogging by impression occurred. The packages became voluminous due to the folded portion so as to raise transportation cost and corrugated board cost. The compressive strength and dropping strength of the packaging bag became lower, and therefore, the packaging material of FIG. 19 was only used for gusset bags.